A diamond blade is used for cutting a hard and brittle material such as stone or concrete. A general example of this blade is a segmented blade shown in FIG. 12 formed by providing slots on the outer peripheral edge of a circular core while providing superabrasive layers on portions of the outer peripheral surface located between these slots, and the superabrasive layers are prepared by bonding superabrasive grains to each other through a metal bond or the like. The superabrasive layers are bonded to the core by brazing, welding or simultaneous sintering for bonding the superabrasive layers to the core simultaneously with sintering.
The superabrasive layers of the blade have recently been reduced in thickness, and the thickness of the core must also be reduced following this. When the thickness of the core is reduced, dust resulting from cutting enter clearances between the core and cutting grooves to wear particularly portions around junctions between the core and the superabrasive layers (hereinafter referred to as undercutting), leading to a significant problem. In other words, a thin core may be broken if worn with dust, while no problem arises in a thick core even if the core is worn with dust and slightly reduced in thickness.
Japanese Patent Laying-Open No. 8-90425 describes a blade preventing the aforementioned undercutting. FIG. 13 shows this blade. This blade is formed by providing a plurality of slots on the outer peripheral edge of a core and fixing superabrasive layers to portions of the outer peripheral surface located between the slots while providing extensions by partially extending the superabrasive layers toward the inner periphery of the core, in order to prevent the undercutting in a segmented blade.
Further, Japanese Patent Laying-Open No. 11-207633 describes a large-diameter blade of at least 250 mm in diameter preventing undercutting while preventing a core from wobbling in cutting. FIG. 14 shows this blade. This blade is formed by providing extensions by partially extending superabrasive layers toward the inner periphery of a core while mounting a plurality of core reinforcing diamond segments radially formed with a prescribed width on substantially intermediate positions between the outer periphery of the core and the center of the blade at prescribed intervals.
However, the aforementioned blade mounted with the core reinforcing diamond segments depends on the reinforcing diamond segments for preventing wobbling during cutting, and hence prevention of wobbling is limited and not necessarily satisfactory. In other words, the core is reinforced due to the rigidity of the radially formed diamond segments and hence circumferential rigidity of the core tends to be insufficient although radial rigidity is improved, to possibly cause wobbling. Further, the diamond segments are provided on the substantially intermediate positions between the outer periphery of the core and the center of the blade and hence there is an apprehension that tension adjustment of the core cannot be performed and the core cannot be completely inhibited from wobbling. The tension adjustment of the core is an operation of extending the inner peripheral side of the core with a pressure roll or extending the same by striking with a hammer thereby supplying stress in a direction for spreading the inner peripheral side and providing the outer periphery with circumferential tensile stress with this force. Thus, the outer peripheral side provided with the superabrasive layers serving as inserts is pulled for suppressing wobbling in cutting.
If dry cutting is performed with a blade not subjected to the aforementioned tension adjustment (tensioning), heat is generated around superabrasive layers to disadvantageously expand the core by thermal expansion and wobble the same. While wobbling can be prevented despite slight expansion of the outer periphery if tension adjustment is performed in this case, the aforementioned blade causes this problem due to impossibility of tension adjustment. Therefore, cutting must disadvantageously be frequently interrupted in order to cool the blade. While the aforementioned blade aims at preventing wobbling with reinforcing superabrasive layers, wobbling is frequently caused due to thermal expansion of the core resulting from heat generation during use of the blade in practice, and hence tension adjustment must be previously performed.